Manufacture of perforated acoustic boards



Dec. 1, 1964 0. w. AKERSON 3,159,236

MANUFACTURE OF PERFORATEID ACOUSTIC BOARDS Original Filed Oct. 6, 1958 2 Sheets-Sheet 1 52 62 63 (5/ 63 61 6 57 6 v PA 60 In 0612 {07 .58 jjam'a' Wflkersorz m/fimw l 6 W L? J! or Dec. 1, 1964 D. w. AKERSON 3,159,236

MANUFACTURE OF PERFORATED ACOUSTIC BOARDS Original Filed Oct. 6, 1958 2 Sheets-Sheet 2 E A DRILLED E 25 Q Q Q E Q B CAVITIZED Ln-l O 20- U C(NON-CAVITIZED) E 15 m g I". .I 1 I l X 1e 17 18 19 AIR-DRY DENSITY (POUNDS PER CUBIC FOOT) 76' 66 II! .J

nvenzor 77 7 Pavia! "(J/M71502? 76 6 9 29 fltzorney snsaass MANUFACTURE or rnarona'rno Acousrrc ensues I David W. Alrerson, St. Paul, Minn, assignor to Wood 6 fllaims. (Cl. 181M315),

The present invention relates to acoustic material, and in particular, to the manufacture of acoustic bodies or panels, such as wallboard, tile and plank.

Heretofore, porous panel-form bodies which have interior capacity to absorb sound have been drilled with holes to collect sound waves and transmit them to the interior of the body. The common practice is to drill round holes of such size that they are visible when present in ceiling tile, and thearrangement of the holes is suc as to form an acceptable pattern.

Where visibility of such holes is undesired, as for example, when other decoration is present at the surface of the tile, a recent practice is to punch small holes with pins or needles, of such diameter that the holes are practically invisible at viewing distance, or otherwise if visible, constitute such a small portion of the containing area that other decoration at the surface subdues'the visible effect of such small holes.

The present invention aims to improve the soundabsorbing capacity of bodies such as ceiling tile in which such small holes are present in the surface for soundabsorption. I

It is an object of the invention to provide at the interior of a porous sound-absorbing body a multiplicity of soundabsorbing cavities so located that each is in communication with the exterior by a channel of relatively smaller size, terminating in a small opening in the surface.

It is a particular object of the invention to provide a cavity wholly inward from both faces of an integral soundabsorbing panel.

It is also among the objects of the invention to provide various methods for producing such openings and cavi ties in sound-absorbing bodies of various materials.

it is a particular object of the invention to produce such openings in the interior of anintegral felted fiber body containing vegetable fibers.

It is also a particular object of the invention to provide means for producing cavitized surface openings in vegetable fiber panels. Various other and ancillary objects and advantages of the invention will appear from the following description and explanation of t e invention as set forth in connection with the accompanying drawings, in which:

FIG. I is a fragmentary perspective view partly in cross section showing a face with openings therein and illustrating two types of cavity formation which occur in a vegetable fiber panel. I

FlG.,2 is a view similar to FIG. 1 showing the type ofcavity formation in a mineral fiber tile.

FlG. 3 is a graph showing the variation in absorption by a series of products similar to FIG. 1, which vary in density.

MG. 4 shows a modification of structure in which two cavities similar to that of FIG. 1 merge into a single cavity.

REG. 5 represents more or less diagrammatically one method of making a modified cavity.

Fit 6 is a perspective view in cross-section taken on the line 6-6 of FIG. 5.

FIG. 7 is a modified form of the invention effected by lamination.

FIGS.'8 through 11 are views of circular shank punches United States Patent 3,159,236 Patented Dec. 1, 1964 ice with enlarged ends to be rotated after stationary insertion in a panel.

FIGS. 12 through 15 are views at right angles to the showing in FIGS. 8 through ll, respectively.

FIGS. 16 and 17 are cross-sectional views taken, respectively, on line 1616 of FIG. 14, and lines l7 17 of FIG. 15.

FIG. l8-shows the preferred punch for vegetable fiberboard.

It is to be understood that the drawings are merely illustrative and are not intended to limit the invention.

In testing the sound-absorbing capacity of fiberboard, such as used in acoustic tile, it was found that the members'of a series of like tile with the same pattern of surface openings of the same sizes, varied greatly in their sound-absorbing capacity. It was determined that the character of the punch used to make the holes was a controlling factor.

Investigation of the variations of punch structure showed that some punches merely pushed the fibers aside forming a hole matching the punch in contour. Other punches formed a cavity within the board larger in size than the opening formed in the surface by the punch. Qther punches delaminated the fiber body.

For example, with reference toa wood fiber insulation board of about 17 lb. per cu. ft. density, the following observations were made: i

- Blunt punches, that is,cylindrical rods with a flat circular end, tend todelaminate the structure by punching an area of felted layers inwardly, which pushed area carries with it adjacent'structure felted into it. With a diameter of inch the effect was barely noticeable. At

inch diameter, delamination is easily observed. At 3 inch diameter the punch completely destroyed the neighboring structure of the board.

Pointed punches having a long taper, with an included angle in the vicinity of 10 to 15 merely formed'a hole in size corresponding to the shape of the punch. Pointed punches havingan included angle of 45 delaminated the board like a flat-end punch. Pointed punches having a short taper at an included angle in thevicinity of 30 formed within the board a cavity of larger size than the hole formed in the surface, the cavity being connected to the exterior by a short tubular channel in the surface layer.

It was discovered that when such a cavity-forming short-tapered punch was provided with a flat end, by grinding off the point, preferably, but not necessarily. at right angles to the axis of the punch, a pear-shaped cavity is formed nearbut inwardly from the surface opening and the cavity is larger than when the punch is not flattened and is pointed. In some instances such punches also form two spaced pear-shaped cavities alined along the path of the punch, the innermost one being the smaller.

well as for the formation of cavities in a vegetable fiberboard is a cylindrical one having a diameterof inch, with a frusto-conical end with a small base having a diameter of 0.015 to 9.020 inch and a wall with an included cone angle. of 30. it appears that the delaminating tendency above referred to enhances the cavitizing action of a pointed punch. The small fiat area of the advancing punch is too small to destroy the board, but it has a rupturing action leading to a larger cavity being formed by the following tapered section. Circular punches are preferred so that the cavity formed is more or less symmetrically pear-shaped, and also for mechanical facility in providing a gang punch and stripper plate.

The action of cavitizing above described in part depends upon the tensile strength and toughnessof individual vegetable fiberswhich are pulled out of their original felted positionos in cavitizing, and compressed in the lower part of the cavity. Sometimes there is a densified body of fiber along the lower portion of a side wall, and sometimes it is in the bottom of the channel left by the punch. When the felted body is made entirely of mineral fibers such as rock wool, the action is different. Mineral fibers are relatively brittle, and break, rather than yield to displacement by the punch.

In cavitizing mineral tile a different form of punch is used. The shape of the cross-section is not important. It may be square, triangular, star-shaped or other irregular form. It may be used without taper and the end may be flat or notched or otherwise varied. A flat end may be either at right angles to the axis or inclined relative to it, thus forming a sharp angular edge to advance into the mineral felt. The advancing edges of the punch at the top layer of the tile cause breakage of fibers to form an entering tubular channel corresponding to the cross-section. The broken fibers are pushed ahead of the advancing face, either directly or at an angle, and these aid the punch in breaking more fibers but at regions laterally of the path of the punch. Thus, a ragged cavity results of size relatively larger than the size of the punch and of the entering opening in the surface.

The cavities formed vary individually in size and shape, apparently as a result of variations locally in the board structure. Sometimes, the internal structure is such that a cavity does not form, but because such fiber boards are relatively homogeneous, the punching of a large number of holes in the same manner assures that substantially all of them have a cavity. The aim is to provide a multiplicity of cavities each connected to at least one of a multiplicity of surface openings. cavities correspond to the characteristics shown in FIG. 1 and FIG. 2.

FIG. 1 represents a fragmentary enlarged view of a vegetable fiberboard cavitized as described. The body has felted wood fibers bonded by having hydrated the fibers before felting, pressing and drying to a density of about 17 lbs/cu. ft. Such boards are commonly coated for decoration, as indicated by the coat 11 and it is prefenred to coat before punching. The coated face is punched as described forming a multiplicity of openings, some being indicated at 12, and others at 13 and 14.

The opening 13 extends as a tubular channel 15 through the coating and through the adjacent layer of the fiber body. Then, the enlarged cavity 16 which is formed is generally pear-shaped tapering away from the surface to a tubular channel 17 substantially matching the drill size. The darkened area 18 represents one location at which a densified fiber mass is deposited. Thus, the cavity has a major portion of its wall area at least as porous as the body of the board.

Some holes formed in the same manner as hole 13, and at the same time in the same board, show two cavities, as illustrated at the opening 14. The upper cavity 20 corresponds generally to cavity 16, but below it there is a tubular channel 21 generally matching the punch in size which channel 21 enlarges to a cavity 22, smaller than cavity 20 and likewise pear-shaped, which second cavity is extended by tubular channel 23 formed by the end of punch. The local variations in formation account for the different results.

In FIG. 2, the numeral 30 represents a tile in which all the fibers are mineral, such as glass fiber or rock Wool, with a decorative coat 31. Merely for the purpose of illustration the surface openings are varied, being circular at 32 and 33, triangular at 34 and square at 35, made with fiat-end rods or punches as described. Hole 33 has a channel 37 matching the punch size through the coating and through the surface layer of the body, and then within the body the hole enlarges as a ragged cavity 38 substantially entirely to the bottom of the hole 39.

When the body portion is made of mixed rock Wool fibers and sulfite fibers, for example, in the proportion of In general, the

to 15 parts, respectively, the cavity formation responds very closely to that of FIG. 2, due to the predominance of the mineral fibers.

Although the cavitized holes are preferably formed in a gang in a suitable press, they may be formed individually and by hand. In so using a hand punch in a vegetable fiberboard, an experienced operator feels the formation of a cavity. At first, there is a build-up of resistance to the pressing force, then the resistance weakens and the punch moves in. The release of resistance indicates the formation of a cavity. In the case of mineral fiber felts, there is no corresponding reaction.

The character of the cavity varies with the density of the board punched. A board of any given density when uncompressed may be compressed within limits and punched while so compressed. Thus, in using a gang punch with a stripper plate through which the punches extend, the character of the cavity may be varied by varying the degree of compression of the board while being punched. This may be accomplished by placing the stripper plate in contact with the face to be punched at varying pressures from zero to some higher pressure, before moving the punches into the board. Pressure of the stripper plate on the punched face is important to prevent lifting of the coating at the edge of a hole by the outwardly moving punch. Compression of a coated board before punching is frequently important to prevent breaking the coat at regions away from the entering punch, depending in part on the density of the board, and in part on the character of the coat, for example, its brittleness.

The density of the board is involved in its sound-absorbency. Sound-absorbency is measured in several different ways of which one has been used for testing products of the present invention, namely, the impedance tube test of American Society of Testing Materials, designated C 384-56T. An area of a board is tested for sound in the following frequencies: 250, 500, 1000 and 2000 cycles per second, and the test values found for each of said frequencies are averaged as tube test coefficient, hereinafter referred to as TTC.

Wood fiberboards of various densities and of one-half inch thickness, all coated, were gang-punched and cavitized with inch diameter punches with the 30 frustoconical end previously described in a random arrangement of 578 holes per sq. ft. FIG. 3 shows the TTC for the various densities. The significance of the results is indicated by the fact that substantially the same values are secured by the same test, using boards of the same character drilled in a random manner with inch and inch diameter drills totaling 319 holes per sq. ft., whereas for the non-cavitized punching, much less absorption occurs.

FIG. 3 is a plot of TTC on the Y axis against density of the board on the X axis, the density being for airdry wood fiberboard in pounds per cu. ft. Graph A represents the TTC for boards with the conventional drilled holes, with a random and mixed pattern of two sizes of drills, namely, inch and inch diameter.

Graph B is a plot of TTC in similar boards cavitized with the preferred type of blunted tapered inch diameter punch above described. It has nearly the same capacity for absorption as the drilled units, but has the advantage of practically invisible openings at viewing distances in a completed installation.

Graph C represents the TTC of similar units punched with non-cavitizing tapered punches of inch diameter. The appearances of the units for graphs B and C are identical, and the value of the interior cavities is represented by the higher 'ITC values of graph B over graph C.

The invention maybe carried out in other ways and with materials not comprising fibers. For example, two or more openings may be formed so that their companion cavities merge. FIG. 4 shows such a case in a wood fiberboard 40 with coating 41 and two openings 42 and "43, with tubular channels '44 and 45 so closely positioned and cavitized'that one cavity 46 is formed by merger of two, the cavity having two tubular chan-- nels 47 and 48 at its bottom matching the end of the punches.

The cavitized' openings of the present invention may be made by a rotary punch. FIG. 5 represents a body 50, which may be made of felted mineral fibers which yield more readily to this variation, or which may be a porous sound-absorbing non-fibrous mineral content, such as expanded perlite as described in US. Patent No. 2,690,594. The body 50 preferablyhas a coating 51 for decorative purposes. A rotary punch 52 is shown positioned as it may have left thebody 50 after having formed opening 53, channel 54 and cavity 55. g The punch is shown as acircular rod 56 with a right-angular terminal arm 57, preferably of triangular cross-section with base 58 upand vertex 59 down, thus providing a tapered arm to punchinto the surface of the board. As used, it is punched in, while stationary against rotation, thus forming an elongation slot opening designated 55. vWithin the board the punch is rotated and lowered, forming cylindrical cavity designated 55.; Then, the rotation of the. punch is arrested in the entering positionand Withdrawn through the slot 53- The released fibers or crumbled body composition maybe shaken out or blown out, or allowed to remain inthe cavity 55.

When a mineral fiberboard is to be cavitized to procient thickness to avoid eventual delineation of cavities beneath it.

It is to be understood that other mechanical expedients may be used to form within a sound-absorbing body cavities of relatively larger size than a relatively smaller entrance to the cavity from the surface exposed to the sound to be absorbed. However, since a precise geometrical form of the cavity is not necessary for its function, the, simple method of entering and Withdrawing a gang of punches as described, is the preferred method. Experience has shown that punches may be designed to form cavities in fiber panels merely by insertion and withdrawal as described, with results substantially the same as may be e'iifected by rotating inserted punches which have laterally extending or other modified end portions. FIGS. 8 through 17 show modified rotatable punches so used, all having circular shanks inch in duce cavities larger than those described in FIG. 2, the

body of the board may bemadewith a great number of shot such as the globules formed with mineral fibers, which are larger in diameter than a rod-punch to form holes in the surface. By chance distribution,

' the rod punches may engage shot and push the same inwardly to form cavities. Such use of shot'rnust be purposeful and is to be distinguished from accidental or occasional shot which may be found in current'mineralfiberboards. i Q

It is not necessary that the channels to the cavities bevnormal to the surface of the. board. A punch may be entered at an angle into the board, thus permitting deeper insertion and resulting in a somewhat different cavity because of the angular relation to the generally horizontal extent of the fibers. A punch so inserted may be moved about the entering hole on an axis normal to the face of the board, thus tov dig out a cavity.

A sound-absorbing panel may be made by depositing a layer of fibers in a loose felt, distributing thereon a multiplicity of removable bodies of size and shape to form cavities, distributing between and over said bodies more fiber and compressing all to an. integrated fiber mass. The bodies may be water soluble, such as rock salt, to be'dissolved after the fibers are permanently felted. They may be water-insoluble and volatile such as naphthalene, or paradichlorobenzol, to be volatilized from a finished board. Then, a decorative coating may be formed, and the coated board punched with a multiplicity of pins of small size'to form acoustic channels connecting with cavities. Where random arrangements of cavities and of pins are employed, a multiplicity of openings, and not necessarily all, will connect with a multiplicity of cavities, and a multiplicity of cavities,

and not necessarily all, will connect with openings.

A further modification shown in FIG. 7 has a laminated structure in which a porous sound-absorbing diameter. I

FIG. 8 represents a punch with a shank of which the end66 is thinned and flattened with a fishtail end 67 and side notches 68. i

FIG. 9 illustrates a shank 79 with its end thinned and enlarged to a paddle-form 71, and with flutes 72 having a cutting action at. the neck of the cavity. The opening formed is a round hole in the center of a narrower slot. p

FIG. 10 showsa hook-form with the end of the shank 74 on the back side of the hook formed by two angular plane faces '75 and 76 as seen in FIGS. 14 and 16. The 1100x177 is tapered like a wedge with sharp edge 78.

FIGyll shows a lateral circular disk 80 at 90 with shank 81, the disk being rounded as shown.

For fibrous boards the straight punch is effective, re-

quiring no form for cavitizing rotation. However, for

non-fibrous porous panels the rotary punches are useful to form eiiective cavities of the general forms herein described. t

FIG. l8 shows the described preferred punch, having a cylindrical shank83, /m-inch in diameter, a frustoconical end 84 with an inclined angle of SO 'and base 85 of diameter in the range from 0.015 to 0.020 inch.

As a result, the face of the acoustic body presents a multiplicity of openings which constitute but a small portion of'the'containing area. Within the body are a multiplicity of cavities, each communicating with'at least one such opening, each cavity being of relatively larger size than the one or more openings communicating therewith, which enhance the sound-absorbing capacity because of the internal enlargement of the entering channel.

The form of the cavity may vary greatly, the important point being that it opens to the atmosphere through an opening which is smaller in cross-section than the.

cavity within the body, the preferred form having a tubular channel providing an elongated bottle-neck opening, and accordingly, they are herein designated as bottleshaped.

The invention may be embodied in numerous ways without departing from the spirit and scope of the invention as expressed in the appended claims.

I claim:

1. The method of forming acoustic openings in a rigid panel of sound-absorbing material having a coat thereon which is non-absorptive of sound, which comchannels through an adjacentlayer of said panel, and further extending and enlarging each of said channels I laterally each to a cavity of relatively greater cross-section within the interior of the panel, the extensionsof said openings being such that said tubular channels provide bottle-neck openings for the cavities.

2. The method of forming acoustic openings in a rigid panel of sound-absorbing material having a coat thereon which is non-absorptive of sound, which comprises forming a multiplicity of sound-receiving openings of relatively smaller cross-section in said coat, and substantially simultaneously extending said openings as parallel-sided tubular channels through an adjacent layer of said panel, and also further extending and enlarging each of said channels laterally wholly within the interior of the panel, said enlargements forming cavities of relatively greater cross-section.

3. The method of forming acoustic openings in rigid panel of sound-absorbing material comprising a felted fiber body predominating in vegetable fibers, said panel having a coat thereon which is non-absorptive of sound, which comprises forming a multiplicity of sound-receiving openings of relatively smaller cross-section in said coat, said openings being formed by dislodging and pushing into the panel the material of the coat and panel at an area of selected size at the face of the coat, and spreading and extending the resulting opening into a parallelsided tubular channel at an advancing angleof about 30, whereby the advancing dislodged material forms a cavity of relatively larger cross-section within the panel at the inner end of a tubular channel.

4. The method of converting to a sound-absorbing structure a body having sound-absorbing porosity and a planar coat thereon which is non-absorbent of sound, which comprises forming a multiplicity of relatively small openings in the coat, forming parallel-sided tubular channels into the body inwardly from said openings at right angles to said coat, and forming cavities within said body by extending said channels into the body in a direction normal to said coat and relatively enlarging the extended channels in the direction parallel to said coat, the relative sizes of said cavity and said channels forming bottleshaped openings.

5. The method of converting to a sound-absorbing structure a body of felted vegetable fiber having soundabsorbing porosity and a planar coat thereon which is non-absorbent of sound, which comprises forming a multiplicity of relatively small openings in the coat through to an adjacent layer, extending the openings depthwise into said body in a direction normal to said coat as parallelsided tubular channels, and extending the channels and enlarging the same laterally, all by inserting a punch into the body to a depth less than the thickness of the body, said punch having a flat entering face, a straight shank portion removed from said end and a section tapering by an included angle of about 30 from said shank portion to said entering face of the punch, said insertion carrying the tapered section through and past said layer and being effective to form a compress of fibrous material ahead of the punch, whereby said compress in moving into the body forms a cavity of size relatively larger in the direction parallel to the coat than the opening in the coat, and whereby said tapering section in passing through the coat laterally compresses the material of said layer adjacent the coat and enlarges and extends the initial opening in the coat as the opening of a tubular channel.

6. The method of converting to a sound-absorbing structure a fragile body having sound-absorbing porosity and a coat thereon which is non-absorptive of sound, which comprises inserting into and through said coat and an adjacent layer of said body a tool having a stationary rotary shank and a lateral projection, said insertion carrying said projection beyond said layer, thereby forming a parallel-sided tubular channel in said layer, then rotating the shank, thereby forming a cavity in said body beyond said channel of greater cross-section than said channel, then while the toolis stationary in the position of its entry withdrawing the tool through said channel, the insertion and the rotation of the tool loosening pieces of the fragile body, which may be removed from the cavity through said channel.

References Cited in the file of this patent UNITED STATES PATENTS 2,562,711 Gessler et al. July 31, 1951 2,667,925 Dalphone Feb. 2, 1954 2,668,123 Copeland Feb. 2, 1954 2,968,327 Mariner Jan. 17, 1961 3,013,626 Brown et al Dec. 19, 1961 3,013,937 Brown et al. Dec. 19, 1961 3,017,947 Eckert Jan. 23, 1962 FOREIGN PATENTS 851,315 Great Britain Oct. 12, 1960 

1. THE METHOD OF FORMING ACOUSTIC OPENINGS IN A RIGID PANEL OF SOUND-ABSORBING MATERIAL HAVING A COAT THEREON WHICH IS NON-ABSORPTIVE OF SOUND, WHICH COMPRISES FORMING A MULTIPLICITY OF SOUND-RECEIVING OPENINGS OF RELATIVELY SMALLER CROSS-SECTION IN SAID COAT, EXTENDING A MULTIPLICITY OF SAID OPENINGS AS PARALLEL-SIDED TUBULAR CHANNELS THROUGH AN ADJACENT LAYER OF SAID PANEL, AND FURTHER EXTENDING AND ENLARGING EACH OF SAID CHANNELS LATERALLY EACH TO A CAVITY OF RELATIVELY GREATER CROSS-SECTION WITHIN THE INTERIOR OF THE PANEL, THE EXTENSIONS OF SAID OPENINGS BEING SUCH THAT SAID TUBULAR CHANNELS PROVIDE BOTTLE-NECK OPENINGS FOR THE CAVITIES. 